Comment on “A special attack on the multiparty quantum secret sharing of secure direct communication using single photons”

In this comment, we show that the special attack [S.-J. Qin, F. Gao, Q.-Y. Wen, F.-C. Zhu, Opt. Commun. 281 (2008) 5472.], which claims to be able to obtain all the transmitted secret message bit values of the protocol of the multiparty quantum secret sharing of secure direct communication using single photons with random phase shift operations, fails. Furthermore, a class of similar attacks are also shown to fail to extract the secrete message.     

Symmetric excitation and de-excitation of a cavity QED system

We calculate the time evolution of a cavity-QED system subject to a time dependentsinusoidal drive. The drive is modulated by an envelope function with the shape of apulse. The system consists of electrons embedded in a semiconductor nanostructure which iscoupled to a single mode quantized electromagnetic field. The electron-electron as well asphoton-electron interaction is treated exactly using “exact numerical diagonalization” andthe time evolution is calculated by numerically solving the equation of motion for thesystem’s density matrix. We find that the drive causes symmetric excitation andde-excitation where the system climbs up the Jaynes-Cummings ladder and descends back downsymmetrically into its original state. This effect is known at low electron-photoncoupling strengths but our main finding is how robust the effect is even at ultra-strongcoupling strength where the JC-model does not give qualitatively correct results. Weinvestigate the robustness of this symmetric behavior with respect to the drive de-tuningand pulse duration.     

A weight-function approach for determining watershed initial conditions for combustion waves

In many generic combustion models, one finds that a combustionwave will develop with a specific wave speed. However, thereare possible initial temperature profiles which do not evolveinto such waves, but rather die out to the ambient temperature.There can exist, in some models, a clear distinction betweenthose initial conditions that do evolve into combustion wavesand those that do not; this is sometimes referred to as thewatershed initial condition. When fuel consumption is consideredto be negligible, analytical methods can be used to obtain theexact watershed. In this paper, we consider the problem of determiningpseudo-watersheds and ascertaining the relationship betweenthese pseudo-watersheds and the exact watersheds. In the processa novel weight-function approach for infinite spatial domainsis developed.     

The dynamics of a central spin in quantum Heisenberg XY model

In the thermodynamic limit, we present an exact calculation of the time dynamics of a central spin coupling with its environment at finite temperatures. The interactions belong to the Heisenberg XY type. The case of an environment with finite number of spins is also discussed. To get the reduced density matrix, we use a novel operator technique which is mathematically simple and physically clear, and allows us to treat systems and environments that could all be strongly coupled mutually and internally. The expectation value of the central spin and the von Neumann entropy are obtained.     

Synthesis and physicochemical characterization of carbon backbone modified [Gd(TTDA)(H2O)]2- derivatives

The present study was designed to exploit optimum lipophilicity and high water-exchange rate (k(ex)) on low molecular weight Gd(III) complexes to generate high bound relaxivity (r(1)(b)), upon binding to the lipophilic site of human serum albumin (HSA). Two new carbon backbone modified TTDA (3,6,10-tri(carboxymethyl)-3,6,10-triazadodecanedioic acid) derivatives, CB-TTDA and Bz-CB-TTDA, were synthesized. The complexes [Gd(CB-TTDA)(H(2)O)](2-) and [Gd(Bz-CB-TTDA)(H(2)O)](2-) both display high stability constant (log K(GdL) = 20.28 and 20.09, respectively). Furthermore, CB-TTDA (log K(Gd/Zn) = 4.22) and Bz-CB-TTDA (log K(Gd/Zn) = 4.12) exhibit superior selectivity of Gd(III) against Zn(II) than those of TTDA (log K(Gd/Zn) = 2.93), EPTPA-bz-NO(2) (log K(Gd/Zn) = 3.19), and DTPA (log K(Gd/Zn) = 3.76). However, the stability constant values of [Gd(CB-TTDA)(H(2)O)](2-) and [Gd(Bz-CB-TTDA)(H(2)O)](2-) are lower than that of MS-325. The parameters that affect proton relaxivity have been determined in a combined variable temperature (17)O NMR and NMRD study. The water exchange rates are comparable for the two complexes, 232 × 10(6) s(-1) for [Gd(CB-TTDA)(H(2)O)](2-) and 271 × 10(6) s(-1) for [Gd(Bz-CB-TTDA)(H(2)O)](2-). They are higher than those of [Gd(TTDA)(H(2)O)](2-) (146 × 10(6) s(-1)), [Gd(DTPA)(H(2)O)](2-) (4.1 × 10(6) s(-1)), and MS-325 (6.1 × 10(6) s(-1)). Elevated stability and water exchange rate indicate that the presence of cyclobutyl on the carbon backbone imparts rigidity and steric constraint to [Gd(CB-TTDA)(H(2)O)](2-)and [Gd(Bz-CB-TTDA)(H(2)O)](2-). In addition, the major objective for selecting the cyclobutyl is to tune the lipophilicity of [Gd(Bz-CB-TTDA)(H(2)O)](2-). The binding affinity of [Gd(Bz-CB-TTDA)(H(2)O)](2-) to HSA was evaluated by ultrafiltration study across a membrane with a 30 kDa MW cutoff, and the first three stepwise binding constants were determined by fitting the data to a stoichiometric model. The binding association constants (K(A)) for [Gd(CB-TTDA)(H(2)O)](2-) and [Gd(Bz-CB-TTDA)(H(2)O)](2-) are 1.1 × 10(2) and 1.5 × 10(3), respectively. Although the K(A) value for [Gd(Bz-CB-TTDA)(H(2)O)](2-) is lower than that of MS-325 (K(A) = 3.0 × 10(4)), the r(1)(b) value, r(1)(b) = 66.7 mM(-1) s(-1) for [Gd(Bz-CB-TTDA)(H(2)O)](2-), is significantly higher than that of MS-325 (r(1)(b) = 47.0 mM(-1) s(-1)). As measured by the Zn(II) transmetalation process, the kinetic stabilities of [Gd(CB-TTDA)(H(2)O)](2-), [Gd(Bz-CB-TTDA)(H(2)O)](2-), and [Gd(DTPA)(H(2)O)](2-) are similar and are significantly higher than that of [Gd(DTPA-BMA)(H(2)O)](2-). High thermodynamic and kinetic stability and optimized lipophilicity of [Gd(CB-TTDA)(H(2)O)](2-) make it a favorable blood pool contrast agent for MRI.